Climate Science and Policy

Climate change and over-allocation of the Colorado River have resulted in difficult negotiations amongst the seven states (Arizona, California, Colorado, New Mexico, Nevada, Utah, and Wyoming) that rely on the river. The Lower Basin and Federal Government recently came to an agreement (May 2023) for voluntary users to conserve water in trade for financial compensation, resulting in an estimated 3 million acre-feet (MAF) of total conserved water by the end of 2026. Southern California imports more water from the Colorado River than any other user. The majority (80%) of California’s 4.4 MAF allotment from the Colorado River is used to irrigate the region’s $11.6 billion agriculture industry, and only 20% is used for municipal water. This study examines the annual consumptive use of the four largest importers of Colorado River water in California from 1964 – 2021 to identify extreme variations and understand the effect that precipitation plays in those variations. This study also focuses on the time period of 2002 – 2003, in which Southern California’s imports were reduced by 1 MAF due to the Quantification Settlement Agreement (QSA), as a proxy to understand what major cuts in imports will mean to California’s agriculture industry today. The study finds that local precipitation had a negative moderate-strong correlation with consumptive use prior to the 2003 QSA in three of the water districts, but a negative weak correlation following the 2003 QSA in all but one district. Reductions from the QSA were widespread but unevenly distributed; Metropolitan Water District decreased its consumptive use by nearly 50% (~0.5 MAF) while Imperial Irrigation District, the largest user of Colorado River water, decreased by less than 6% (0.2 MAF). Irrigated crop acreage (ICA) of all crops decreased by <1% between 2002 and 2003, with the largest decrease in alfalfa at 51,000 acres. Irrigated crop acreage of all crops increased, on average, in the years following the 2003 QSA, even though consumptive use decreased >12%; the ICA of alfalfa had an overall decrease of ~4% while common produce crops increased by ~3%. Similarly, the total water consumed water by alfalfa decreased >13% in the years following the QSA, while the consumptive use of common produce increased nearly 3%. Overall, alfalfa accounted for ~30% of the total irrigated crop acreage and ~44% of total water consumed within the water districts.